Omni-azimuth antenna system



NOV' 23, 1954 G. B. LlTcHFoRD OMNI-AZINUTH ANTENNA SYSTEM 2sheets-sheet@ Original Filed Oct. 29. 1947 INVENTOR 620/965 5./Tcf/Fo/Qo bbs NASA .Nb

Nov. 23, 1954 G. B. LrrcHFoRD 2,695,405

ONNI-AZINUTH ANTENNA SYSTEM original Filed om. 29, 194'? 2 sheets-sheet2 ATTORNEY ormai-Azn/inrn ANTENNA SYSTEM George B. Litchford, ColdSpring Harbor, N; Yj., assig'ioi' to The Sperry Corporation,y acorporation of Delaware Originai application October 29, 1947, SerialNo. 7 $2,722. Divided and this application January 5, 15951,4 Serial No.204,580

17 claims. (ci. 34a-ies;

The present invention relates to antenna systems and more particularlyto antennas for a precision coarsek and ne, omni-azimuth radio beaconThis application is a division of' Patent No. 2,564,703 grantedAugust21, 1951, for an Omni-Azimuth Guidance System.

In the prior art, omni-azimuth directionreferenceV systems have beenconstructed employing a rotating an'- tenna pattern and a timing orreference wave transmitting arrangement; the associated craft-bornereceiving equipment consisting of a radio receiver and a phasecomparisondirection indicator, e. g. a phasem'eter.'y

In such arrangements, azimuthal direction in terms of the azimuthbearing from the fixed station maybe determined within an angle of a fewdegrees if care is exercised in the design and construction of thetransmitting equipment and craft-borne receiving equipment. However,such systems are not sufficiently accurate where very close tolerancerequirements mustrvbe met, as for example in air traffic control formodern highspeed aircraft in congested air trafiiczones, Furthermore,obstacles such as buildings or sharp irregularities in the terrainwithin a radius of a fewmiles from the fixed transmitting station havebeenv found to cause appreciable angular errors in the directiondeterminations afforded with these prior art systems. Thesev troubleshave been particularly noticeable where a large low-'frequency fixedantenna array such `as an Adcock array was supplied withsuccessively-varied energy components for effecting vertical-axisrotation of a radiation pattern lobe.

An object of the present inventionV is to provide improved omni-azimuthdirection reference apparatus;

Another object of the invention is to provide a rotatable coarse andfine radiation pattern.

A more specific object is to provide an antenna for omni-azimuthdirection reference system characterized by more precise angularindication than heretofore obtainable with omni-azirnuth systems -ofsingle-lobe radiation'patterns, and of accuracy capabilities in. highcontrast to those of prior, low frequency systems.

Yet a further object is to provide an omni-azimuth direction determiningantenna system wherein tendencies toward introduction of azimuthindication errors due to the presence of electromagnetic wave reflectingbuilding' or hills or other irregularities of the terrain intheneighborhood of the fixed reference station are substantiallyeliminated. l

The present' invention overcomes the above shortcornings or prioromni-azimuth systems by the arrangement of the transmitting antenna toprovide a rotating pattern characterized not only by a single-lobe orlimacon-like general form but also by 'a scalloped or multilingeredoutline superimposed thereon, and by transmission and reception of tworeference phase signals of integral frequency ratio. One ofthe referencesignals has a period equal to the period of rotation of the directivepattern and the other has va'period shorter than the period of thefirst, in the ratio of the number' of fingers superimposed upon thegeneral shape of the lobe. In the craft-borne receiving equipment, thephases are compared both as to the long-period waves and as to theshort-period waves introduced by the several fingers, and high azimuthalaccuracy is achieved as well as greatly reduced error due to obstaclesor irregular terrain. This accuracy and independence of terrain errorsis enhanced by reliance upon physicalrotation: ofsuchzparts vof theantennaisystemi asr are: instrumentaly nited States atent ice 2 indetermining the azimuthal energy distribution pattern', yand bycontrolling trie vertical-plane energy dis*- tributionpattern in such away as to concentrate most of the transmitted energy in angles ofelevation above the horizontal.

Referring now to the drawings, a

Fig. l is a diagram of an omni-azimuth transmitting station. y

Fig. 2 is a polar plot of the azimuthal intensity d istribllsition1pattern radiated by the transmitting antenna 1n 1g.

Figs 3, 4 and 5 are oblique, elevation and sectionalviews, respectively,of an antennawunit suitable for generating the azimuthal pattern of Fig.2. k p

Fig. 5a is an alternative three-dipole antennajunit which may beemployed in the antennaof Fig.- 5 instead of the double arcuate dipoleand reflector antenna unit.

Fig. 6 is an elevation of the entire fixed-station ari:-k tenna system,parts being broken away to show the construction thereof;

Fig. 7 is an enlarged view of a section of the lens incorporated in theantenna system of Fig. 9; and Y Fig. 8 is a vertical-plane directivitypattern resulting from the use of the antenna system of Fig. 9*.A

In the fixed transmitting station of Fig. l, an oscillator and frequencymultiplier unit 101 is provided for supplying radio-frequency excitationpower to a radio frequency amplifier 105 having itsroutput circuitarranged'^ to drive a frequency multiplier and radio frequency poweramplifier 107. The power amplifier 197 supi-vlies output power through acoupling to a' rotatably supported antenna system 1119 arranged to berotated at high speed by a driving Vmotor 111; e. g. at 165()- R. P;

The-transmitting antenna 109 is illustrated in Fig. 3 as constructed ina shape generally resembling avvertical-l axis drum, and the details ofthis antenna may be as shown in Figs. 3-5, for producing an azimuthalradiant energy distribution pattern generally according to Fig. 2.

The rotatable transmitting antenna 1G9-is of such design as `to providean azimuthal radiation pattern 'substantially as shown in Fig. 2. Thispattern is characterized by a scallop plane of n fingers, where n ispreferably an odd number, e. g. 1l. Such a pattern may be produced bythe use of a double arcuate dipole and reflector central antenna with aspecial `n-fi'ngerpattern fringe modifier, as shown in Figs. 3, 4 and 5.Two arcuate doublet or dipole parts 404 and 406 are provided (seeespecially Fig. 5), each having one arcuate arm connected to the outersheath 403 of a coaxial feed line and the other arm connected to theinner conductor 40S of the coaxial line. These arcuate dipoles eachoccupy a sector about the vertical axis of the system, at a radius ofapproximately l/t wave"- length. A conductive reflector plate 498' issupported on an arm extendingback from the outer sheathe, this platebeing` spaced approximately 1A: wavelength` from the axis of the systemand being positioned directly opposite the two arcuate dipoles. Thedimensions of the reflector plate, in terms of wavelength, may beapproximately 1A wavelength high by 1A.. wavelength wide. The centralunit comprising antenna elements 46M, 406, and 403 produces a limaconpattern, the shape of which is indicated in dotted line 41 in Fig. 2.

These elements are positioned at the middle ofa drum formed with upperand lower conductive plates` 411 and 413, which serve together as a waveguide for guiding the energy from the central unit 401 to the peripheralaperture. Vertical staves or columns such'fas column 415 are providedfor distorting the fringe of the limacon'- shaped pattern in such amanner as' to provide it scallops or fingers therearound for achievingfine-and-c'oarse modulation frequency control features, the resultantazirnuthal directivity pattern of unit 109 being as shown at 43 in Fig.2. These n vertical bars may be made of dielectric material or of asemi-conductor, as desired, since the fringing can be accomplished byany* such' elements as will causeA regular alternations aroundl abetween "'thefperipheries of .platesl 411 and 5413:-

n alternative central antenna unit 19 shown in Fig. 5a may be employedinstead of the double arcuate dipole and reflector antenna unit 401shown in Fig. 5. This alternative antenna unit comprises three dipole ordoublet antenna portions 21, 23 and 25, as shown in Fig. 4 of myapplication S. N. 782,721, led October 29, 1947, now Patent 2,567,220.Each of the dipole portions have two arcuate arms rigidly supported onparallel arms extending outward from the outer conductor 15. Alternatearcuate arms, e. g. the clockwise arcuate arms of the dipoles 21, 23, 25are connected by radial conductors 31, 33 and 35 to the inner conductor17 of the coaxial transmission line. These radially extending conductorspass through clearance holes in the outer conductor 15.

A shorting bar 37 is provided for affording a current path betweenradial conductor 35 and the substantially radial rigid arm 39. Withoutsuch a bar 37, the three arcuate dipole systems 21, 23, and 25 would beenergized cophasally and in equal intensities, producing a generallycircular intensity pattern. The shorting bar 37 is provided fordistorting the radiation pattern of the antenna unit 19, to reduce theintensity in the direction of conductor 35, and to give the radiationpattern a general limacon-like character. The nature of the radiationpattern produced by the inner unit 19 alone is illustrated in dottedline at 41, Fig. 2, the minimum-radius portion thereof corresponding tothe direction of the radial conductor 35.

Returning now to Fig. l, two alternating voltage generators 113 and 115are coupled to antenna 109 so that their rotors revolve in lixedrelation therewith. These generators may comprise permanently magnetizedrotors and cooperating stator output coils. Generator 115 is providedwith a two-pole permanently magnetized rotor, while generator 113 isprovided with a rotor characterized by n pairs of poles, or a statormade up of n dual-pole sections. Generator 115 produces output voltageat the frequency of rotation of antenna 109, while generator 113produces output voltage of n times the frequency of rotation. For thispurpose, generator 113 may if desired be a simple generator geared tothe rotor of generator 115 through n ratio gears. The voltage fromgenerator 115 provides a reference for comparison with the rotationfrequency modulation component due to the general lirnaconlike shape ofthe antenna pattern, and the output voltage of generator 113 provides aphase reference signal for phase comparison with the high frequencyamplitude modulation component observed in any azimuth direction due tothe n scallops around the fringe of the directional pattern.

These reference phase voltages from generators 113 and 115 are added andamplified in unit 117, and impressed by frequency modulation upon asubcarrier signal generated in an oscillator unit 119. This frequencymodulated subcarrier signal is in turn supplied to the input terminalsof an amplitude modulator 121 coupled to unit 105 for introducingsubcarrier modulation into the output energy radiated through antenna109. The subcarrier modulation arrangement described above is merelyillustrative of the arrangements which may be used for transmittingphase reference signals to the craft. Another way to accomplish thephase reference signal transmission is by frequency modulation of unit101 according to the phase reference signal wave, as set forth in U. S.Patent 2,377,902 to M. Relson.

A receiving system and azimuth direction indicator for responding to thetransmitter of Fig. l is set forth in the above mentioned Patent 2,564,703.

To attempt to extend the rotatable antenna unit into a structure ofgreat height for sharp vertical-plane directivity would be difficult,and would involve serious problems in making such a system dynamicallybalanced for high speed rotation. According to a further feature of thepresent invention, the sharp vertical-plane directivity is accomplishedwithout any vertical extension of the rotating unit, by a cylindricallens system which surrounds the rotating antenna unit 109 and remainsstationary. This permits the multi-fingered and limacon-like pattern tobe revolved according to the rotation of the vertically pivoted antennaunit, and affects only the vertical-plane energy distribution.

Such a lens system is illustrated at 202 in Figs. 6 and 7. This lenssystem surrounding the rotatable antenna 109 provides a vertical-planedirectivity pattern as illustrated at 204 in Fig. 8. The completeantenna system is shown in a vertical elevation view in Fig. 6, partsbeing broken cli away to provide a clearer view of the honeycombedconstruction of the cylindrical lens and also to show the position ofthe rotatable antenna unit in relation thereto, and a portion is shownin magnified view in Fig. 7. The rotated structure may be supplemented,if desired, by a biconical horn 206, 208, for concentrating the energyfrom the rotatable antenna unit 109 toward the inner cylindricalboundary of the lens 202. Biconical horn 206, 20S preferably is madestationary, with slight clearance for freedom of rotation of unit 109.

The horizontal membranes of the lens 202 are made up as annular metallicdiscs which may be made with their inner diameters uniform and theirouter diameters varied as required according to knownultra-high-frequency lens design techniques.

The antenna system may be supported on a tower and the lens there aidsin preventing energy going downward to impinge on roofs of lowbuildings, e. g. hangars, to be reflected therefrom and tend tointroduce minute angular error in the system indications.

Representative dimensions for the antenna system for operation at afrequency of the order of 5000 megacycles are as follows:

Outer diameter of coaxial line 403, 405, Ss.

Diameter of drum unit 109, l0".

Radius of the dipole arms, 1%.

Spacing of the reflector from the axis to the shaft, 1%".

Height of the reflector, 1/2".

Length of the reector, 1%.

Spacing between the upper and lower discs of the rotating drum, 2".

Height of the lens system, 15.

Diameter of the lens system, 25.

Location of the drum, approximately central in the lens system.

Vertical spacing of the horizontal membranes in the lens system, ll/'z".

Angular spacing between radial vertical fins in the lens system, approx.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. An antenna system comprising two substantially circular mutuallyparallel conductive plates spaced apart along a common axis, means foremitting ultra-high-frequency energy at the substantially central regionbetween said plates for radial propagation of said energy to theperipheral region and thence into external space, and

phase front distorting means for introducing a plurality of similarvariations of phase delay in the radial propagation at regular angularintervals around the peripheral region between said plates.

2. An antenna system as defined in claim l, wherein saidultra-high-frequency energy emitting means comprises means for directingenergy in a limacon-like pattern to define opposite directions ofmaximum and minimum intensity and regular gradations of intensitythroughout the angular ranges of directions therebetween.

3. An antenna system as defined in claim 2, wherein said energydirecting means comprises at least one set of three doublets each fed bya two-conductor radial feeder, the three doublets together with saidfeeders lying in a plane parallel to said parallel plates, at least oneof the feeder conductor pairs being shorted, and an ultra-highfrequencyenergy source being connected to at least one of said feeder conductorpairs.

4. An antenna system as defined in claim 3, wherein each arm of each ofsaid doublets is arcuate and all of the six arms of said three doubletsare oriented in successive 60 arcs of a circle in said plane.

5. An antenna system as defined in claim 4, wherein said phase frontdistorting means comprises a plurality of columns extending between saidplates in the region of their peripheries and spaced at intervals ofsubstantially equal angles around said axis.

6. Radiator apparatus for producing a rotating asymmetrical azimuthalpattern for craft guidance, comprising a vertical-axis rotatable antennaassembly characterized by an asymmetrical energy distribution about said5 vertical axis, and an annular ultra-high-frequency lens surroundingsaid assembly coaxially therewith for restricting the vertical planeenergy distribution to a predetermined vertical-plane pattern.

7. Radiator apparatus as defined in claim 6, further including abiconical first vertical pattern energy director coaXially surroundingsaid rotatable antenna assembly internally of said annular lens forconcentrating the energy from said assembly toward said lens.

8. Radiator apparatus for producing a rotating asymmetrical azimuthalpattern for craft guidance, comprising a vertical-axis rotatable antennaassembly characterized by an asymmetrical energy distribution about saidvertical axis, and stationary annular directive means surrounding saidrotatable assembly coaxially therewith for restricting the radiationdirections to a narrow range of angles of elevation, said means being soarranged as to leave the azimuthal-plane energy distributionsubstantially unaltered.

9. In a coarse and ne omni-azimuth beacon system, means to radiate afirst directional radiation pattern comprising a pair of dipoles and areilector arranged to provide a limacon-shaped pattern, means tosuperimpose projections on said pattern comprising a plurality ofvertical struts uniformly arranged in a circular manner about saiddipoles, and a high speed motor connected to rotate said dipoles andsaid reflector to thereby provide a rotatable coarse and fine pattern.

10. An antenna system as defined in claim 9 wherein the means to radiatethe coarse and fine pattern also includes a pair of parallel platemembers disposed above and below the dipoles and the struts and arrangedto restrict the vertical angle of the radiation pattern.

11. An antenna system as defined in claim 9 wherein the rotating dipolesand struts are disposed within a biconical horn.

12. An antenna system as defined in claim 10 wherein said rotatingdipole struts and said parallel plates are enclosed within a stationarymicrowave lens for the purpose of restricting the vertical angle of theradiation pat1 tern.

13. An antenna system having means to radiate a rotatable coarse andline radiation pattern comprising, a plurality of rotatable radiatingelements and a reector for providing a directional pattern, a pluralityof thin members uniformly arranged around said radiating elements formodifying said pattern to provide a plurality of projections around itsedge.

14. An antenna system as defined in clairn 13 wherein the means toradiate the coarse and fine patterns also includes a pair of parallelplate members disposed above and below said horizontal elements andarranged to restrict the vertical angle of the radiation pattern.

15. An antenna system as defined in claim 13 wherein he rotatableelements are disposed within a biconical orn.

16. An antenna system as dened in claim 14 wherein said rotatableelements and said parallel plates are enclosed within a stationarymicrowave lens for the pnrpose of restricting the vertical angle of theradiation pattern.

17. An antenna system for radiating a rotatable coarse and fine patterncomprising, a radiator and a reilector, at least one of which isrotatable, and a plurality of struts uniformly arranged about saidradiator in the direction of radiation for providing a scalloped edge tothe radiation pattern of said radiator.

References Cited in the tile of this patent UNITED STATES PATENTS NumberName Date 2,461,187 Steinmann Feb. 8, 1949 2,536,509 Luck Jan. 2, 1951FOREIGN PATENTS Number Country Date 581,576 Great Britain Oct. 17, 1946

